Scientists have recently found new information about an everyday problem for most people; allergies. Most people are affected by gentle, yet annoying, symptoms such as itching, sneezing, sore eyes and runny noses. Many people are prepared for these symptoms seasonally. In fact, 1 in 50 people have serious reactions to certain allergens, like bee stings. These severe reactions could actually be lethal, and is called anaphylaxis.
Scientists have still got a lot of questions about allergies themselves, even though allergies are so common today. Some questions, such as what makes different substances potentially allergenic, or not? and even why does the allergic response to certain substances exist at all? And does it serve any evolutionary purpose at all?
In 1991, Margie Profet at the University of California, thought that allergic reactions and responses could have evolved to ‘enable the immune system to protect us against environmental toxins’, including natural toxins found in certain plants and venoms. This could actually be true, as many allergens are actually thought of as toxins. So, allergic reactions are seen as a beneficial response that protects us against harmful substances within the environment.
The New Scientist article says ‘But the toxin hypothesis remains largely ignored by the biomedical community. We think this is wrong-headed for four reasons. First, allergic symptoms, including runny nose, tears, sneezing, vomiting and diarrhoea, can be understood as an attempt by the body to get rid of an allergen. Toxic substances found in the food and air elicit similar expulsive reactions in everyone.’ So, as only some people pose allergic reactions to certain substances, toxins should make everybody have the same reactions, but this doesnt happen.
But, allergic responses to allergens are immediate, and usually happen within minutes or seconds after exposure. This is consistent with defense against toxins. However, many people can become hypersensitive to certain allergens, and ‘given that even immune responses to bacterial and viral pathodgens doesnt reach this level of sensitivity’, this does not make sense.
The most puzzling aspect of an allergic response is the ‘diversity of substances that act as allergens’. The allergens can be anything from tiny molecules in certain medicines, to complex substances found in venoms, or common foods like peanuts. The toxin hypothesis shows that what these substances share is their ability to cause harm or damage to the human body.
But even if it was accepted that allergic reactions happened only to protect us from toxins, why would there be severe, potentially lethal, reactions that could kill us? Doesn’t that defeat the point?
This, however, could have been useful to our ancestors. As people who actually suffer from allergies know, you should leave the area which provokes the reactions. So, ‘if many allergens are toxic, then the allergic reactions could be interpreted as conditioning people to avoid harmful environments’.
Apparently, in rare cases, allergies can become conditioned in the nervous system. “For example, someone allergic to flowers may reach a point where they show an allergic reaction to a mere picture of a flower.” This does make some kind of sense as most of the sources of pathogens can actually be identified by sight, which could mean that the body has developed an avoidance strategy.
So, in conclusion, these painful reactions could be to convince the body to avoid the areas or substances that contain pathogens or could cause harm to the body.
“Likewise, allergies may have evolved to feel unpleasant to encourage us to avoid environments, animals, or foods that contain substances that may harm us.”